convert iphone3gs to itouch

[cfli1688c1]

I just brought a iphone 3gs. I have to do a restore using itunes.
I am not looking to use it as a phone, just as an itouch to use wifi and games.
It is not at the activate page. I have a t-mobile pre-paid card.
I am not sure how to proceed.
Is there a way to activate it with the t-mobile pre-paid card?

Thanks.